1. Field of the Invention
The present invention relates to a finger opening and closing mechanism for a tool exchanging device of a machine tool, particularly to a finger opening and closing mechanism for a tool exchanging device of a machine tool for exchanging tools set to a spindle and a tool magazine of a machine tool.
2. Description of Related Art
There has been conventionally known a machine tool capable of exchanging tools between a spindle and a tool magazine. According to the machine tool, a finger opening and closing mechanism of a tool exchanging device for exchanging tools is installed, tools respectively set to a spindle and a tool magazine are grasped by pairs of fingers installed to a main body thereof, and positions of the tools are changed and tools are exchanged by pivoting a tool exchange arm.
There has been known a finger opening and closing mechanism of this kind disclosed in JP-A-3-92238 and U.S. Pat. No. 4,883,772 where a center shaft mounted with finger driving cams is separately installed at the inside of a hollow pivoting shaft for pivoting a tool exchange arm, which has a comparatively simple constitution and which accurately regulates motion of fingers, whereby pairs of fingers are opened and closed by pivoting the center shaft by a predetermined angle.
FIG. 1 shows a conventional finger opening and closing mechanism When a tool exchange device drive shaft (hereinafter, referred to as an ATC drive shaft) 118 is driven to rotate by a tool exchange drive motor 115, a rotational motion of a cylindrical groove cam 123 provided on the ATC drive shaft 118 is converted into a vertical reciprocal motion of a cylindrical member 136 via a pivoting lever 140 whereby a tool exchange arm main body 116 is vertically reciprocated along with a hollow spindle 125 fitted to the cylindrical member 136.
Further, rotation of parallel cams 121 provided on the lower portion of the ATC drive shaft 118 is converted into pivoting of a spline sub shaft 137 via follower rollers 138 whereby the hollow spindle 125 in mesh with the spline sub shaft 137 is pivoted thereby pivoting the tool exchange arm main body 116.
Meanwhile, rotation of a plane groove cam 124 installed at the highest position of the ATC drive shaft 118 converted into pivoting of a segment gear 134 via a pivoter 135 whereby an arm center shaft 131 fixedly fitted to a support member 129 in mesh with the segment gear 134 is pivoted. At this moment, a hollow cam shaft 151 fitted to the arm center shaft 131 at the lower portion of the arm center shaft 131 is pivoted, and the pivoting force is transmitted to driven portions 117C of pairs of fingers 117 whereby gripper jaws or claw portions at front ends of the pairs of fingers 117 are opened and closed.
However, according to such a finger opening and closing mechanism, the pivoting shaft must be fabricated in a hollow shape and accordingly, the fabrication cost is increased. Further, the center shaft for opening and closing the claw portions at the front ends of the pairs of fingers requires a slender shape since it is incorporated at the inside of the pivoting shaft. Accordingly, strength of the shaft in respect of torsion is small, and it is conceivable that even if a pivoting angle of the center shaft is set, the opening and closing angle of the claw portions at the front ends of the pairs of fingers is not brought into a predetermined value. Therefore, the center shaft needs to be pivoted excessively in consideration of the torsion.
Also, the life of the center shaft may be shortened by the torsion and so on. A large plane pressure may be applied since the diameter fitted thereto is small and a large torque cannot be obtained.